The oxidation of alcohols to carbonyl compounds is an important transformation in organic chemistry and, as such, numerous preparative methods have been developed for this purpose. Traditionally, oxidation of alcohols is carried out with heavy metal reagents such as chromium (VI), ruthenium, manganese (VII) or with peroxyacids, activated dimethyl sulfoxide (DMSO), and hypervalent iodine. Often, these processes are conducted under harsh reaction conditions with expensive reagents and generate large amounts of toxic waste, rendering them impractical for most large-scale industrial application. Additionally, the reaction conditions generally used in these methods are insensitive to independently reactive functional groups such as unsaturated carbon-carbon bonds, thereby severely limiting their use in synthetic organic chemistry.
Stable tetraalkylnitroxyl radicals, such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) have been used for oxidation of organic alcohols as described, for example, by Annelli (J. Org. Chem. 1987, 52, 2560) and Ciriminna (Org. Process Res. Dev., 2010, 14, 245). However, known processes employing TEMPO-mediated oxidation for the preparation of carbonyl compounds with labile functional groups, such as alkenes, are generally associated with disadvantages including expensive terminal oxidants (e.g., iodosobenzene diacetate), stoichiometric amounts of TEMPO, environmentally unfriendly chlorinated solvents, and impractically long reaction times. Accordingly, there is a need in the art for alcohol oxidation methods that are high yielding, selective, and robust, yet are conducted under mild reaction conditions and are tolerant of independently reactive functional groups, such as unsaturated carbon-carbon bonds. The present invention satisfies this need and provides other advantages as well.